Prior art bipolar transistors typically comprise a heavily doped buried layer that is located under a lightly doped epitaxial layer (epi layer). The epi layer provides high breakdown and the buried layer provides low resistance. A heavily doped sinker is often used to provide a low resistance path between the buried layer and an external collector contact.
Breakdown voltage is directly proportional to the thickness of the epi layer. Therefore all vertical bipolar transistors that have the same epi layer thickness will have the same breakdown voltage. Breakdown voltage generally has an inverse relationship to operating speed and series resistance.
There are some circuit applications in which it would be desirable to have some bipolar transistors that have a first value of breakdown voltage and some other bipolar transistors (in the same integrated circuit) that have a second (different) value of breakdown voltage. In this way, those transistors with lower breakdown voltage requirements could have faster speeds and lower series resistance. Prior art bipolar transistors are not capable of having more than one value of breakdown voltage.
Therefore, there is a need in the art for a system and method for manufacturing a bipolar transistor that is capable of having more than one value of breakdown voltage. That is, there is a need in the art for a system and method for manufacturing a bipolar transistor that is capable of having one of a plurality of possible breakdown voltages.